In the past, to maintain the flowable substance free of contaminants, preservatives have been mixed in with the flowable substance in the reservoir from which it is to be dispensed. The use of preservatives tends to be detrimental to users and often limits the effectiveness of the flowable substance, particularly when the flowable substance is a pharmaceutical such as an eye care solution, an intranasal drug, cosmetic treatment or skin treatment product. This group of prescription and nonprescription medications are often formulated with preservatives in multi-dose formats. The flowable substance may also be a food stuff, a beverage, a nutraceutical or cosmeceutical product.
Another consideration is the ability of the valve assembly to deliver a selected amount of the flowable substance to the outlet without causing any damage to the user, such as when applying an eye care solution directly into the eye.
In the past, flexible membranes have been used to control the flow of the flowable substance to the valve assembly outlet while preventing any backflow to the source of the flowable substance. However such valves, such as the valve described in U.S. Pat. No. RE34,243, which is incorporated by reference herein in its entirety, describe the use of O-rings in conjunction with a uniformly thick flexible membrane to effect a seal. Other valve assemblies also used cylindrical parts which required, for example, sliding the pretensioned flexible membrane over the straight sided core during assembly, preventing automated high speed assembly. Therefore, an effectively designed valve assembly which was able to be manufactured, for example via high speed automated production, and limited the costs of manufacture by reducing component parts and allowing the use of high speed automated production, was not provided in the past.